The present invention relates to a screw tool.
A screw tool is known from Federal Republic of Germany OS 3 344 361, in which the driven core part of triangular cross section forms with the outer drive ring part the wedge-shaped clamping spaces for the reception of roller-shaped clamping members arranged in pairs. Between each pair of clamping members there extends a compression spring which acts on them and presses the clamping members into the wedge-shaped clamping spaces. The shifting of the clamping members in order to obtain different directions of drive is effected by means of the centrally mounted switch member from which drivers bent off at an angle extend. In this connection, three such drivers are provided, they extending in each case between a pair of the clamping members. For the free rotatability of the drivers the triangle corners are cut off concentricaly to the center of rotation so that the drivers can move there into the adjacent clamping spaces, regardless of the direction in which the driving of the driven core part is desired. For the fixing of the switch member in its switch positions there is provided a detent ball which is arranged in the driven core part and which cooperates with the switch member. Aside from the structural shape which is expensive from a standpoint of manufacture, as a result of the large number of structural parts, unfavorable frictional conditions exist which upon longer use of the screw tool, lead to premature phenomena of fatigue.